Power steering system for a vehicle provided with means for actuating the stop and start function in a moving vehicle, especially an industrial or commercial or special vehicle

ABSTRACT

The present invention relates to a power steering system for a vehicle provided with means for actuating the stop &amp; start function in a moving vehicle, especially an industrial or commercial or special vehicle, said vehicle being equipped with hybrid drive of the parallel type, comprising a thermal engine ( 1 ), an electric motor-generator ( 2 ), a single clutch unit ( 3 ) placed between the two engines, a transmission system ( 6 ) comprising an automated manual transmission, the method comprising the steps of enabling of the stop phase, activation of the stop phase, maintaining of the stop phase, activation of the start phase, the system comprising a hybrid power steering with coupling of a hydraulic power steering controlled by the thermal engine, and an electric power steering controlled by a control system (EPS) of the electric power steering.

APPLICATION FIELD OF THE INVENTION

The present invention relates to a power steering system for a vehicleprovided with means for actuating the stop & start function in a vehiclewhile moving, especially an industrial or commercial or special vehicle,and more precisely in a vehicle equipped with hybrid drive of theparallel type, with single clutch.

DESCRIPTION OF THE PRIOR ART

With reference to FIG. 1, a type of industrial or commercial or specialvehicle equipped with hybrid drive of the parallel type is known in theart, comprising a thermal engine 1, an electric motor-generator 2,equipped with a DC/AC inverter and a high-tension electric drive battery5, a single clutch unit 3 placed between the two engines, and atransmission system 6 comprising an automated manual transmission. Thelatter is substantially a mechanical gearbox wherein electric actuatorsare present and are controlled by a specially provided control unitwhich manages the shifting requests and the clutch control, according tothe drive management strategies of the two engines, thermal andelectric.

In this type of vehicle the following operating modes are known:

-   -   Stop & Start function: The thermal engine is stopped when zero        speed is reached. When the brake pedal is released, the thermal        engine is quickly and independently restarted by means of the        motor-generator.    -   Electric launch function and creeping: The vehicle starts moving        by means of the electric motor keeping the thermal engine idle        at each restarting; the motor-generator is also used to move the        vehicle at low speed (creeping), a phase in which the thermal        engine is highly inefficient.    -   Hybrid mode (electric power boost) of the parallel type: The        power required for moving the vehicle is provided by combining        the contribution of the electric motor and of the thermal engine        (torque split). When the power of the vehicle temporarily        increases and the thermal engine contribution is not enough, the        electric motor provides the missing power (booster).    -   Regenerative braking function: The kinetic energy of the vehicle        is converted, during the braking phases, into electric energy by        the motor-generator and is stored in the high tension electric        drive battery by means of the inverter.    -   Static mode with stationary vehicle: The thermal engine is        stopped. The energy stored in the battery is used to power some        auxiliary devices of the vehicle by means of the power takeoff        PTO directly activated by the electric motor-generator (e.g.:        waste collection vehicle).

In order to improve the vehicle's functionalities as for, above all, thereduction of fuel consumption and of pollutant emissions and also ofnoise emissions, a further operating mode would be provided consistingin the stop & start function while the vehicle is moving, thusincreasing the time percentage in which the electric motor is workingand the thermal engine is stopped.

Problems arise relating to the management of the operating logic of thetwo engines in order to control said stop & start function in a movingvehicle, namely the stopping and restarting of the thermal engine whilemoving, due above all to the presence of a single clutch unit, and alsoproblems relating to the power steering, since when the thermal engineis stopped the hydraulic power steering does not work.

The use of a completely electric steering actuator is known in the art,since the electric actuation is able to operate the power steering whenthe thermal engine is stopped, with any speed condition of the vehicle,both low (or zero) speed and high speed.

Presumably, in a parallel hybrid vehicle equipped with dual clutch, oneupstream and the other downstream of the motor-generator, the managementof the stop & start function with a moving vehicle would be easier.

SUMMARY OF THE INVENTION

Therefore the aim of the present invention is to provide a powersteering system for a vehicle provided with means for actuating the stop& start function in a moving vehicle, especially an industrial orcommercial or special vehicles, suitable for overcoming all thedrawbacks mentioned above.

In particular the subject of the present invention is a power steeringsystem for a vehicle provided with means for actuating the stop & startfunction in a moving vehicle, especially an industrial or commercial orspecial vehicle, as described more fully in the claims, which are anintegral part of this description.

BRIEF DESCRIPTION OF THE FIGURES

Further purposes and advantages of the present invention will becomeclear from the following detailed description of a preferred embodiment(and its alternative embodiments) and the drawings that are attachedhereto, which are merely illustrative and non-limitative, in which:

FIG. 1 shows a general scheme of a drive system of a vehicle suitable torealize the method according to the invention;

FIG. 2 shows a block diagram of the main vehicle functions involved inactuating the method according to the invention;

FIG. 3 shows an embodiment of the power steering device;

FIG. 4 shows a flowchart of the operations for enabling the stop phaseof the method;

FIG. 5 shows a flowchart of the operations for actuating the stop phaseof the method;

FIG. 6 shows a flowchart of the operations for maintaining the stopphase of the method;

FIG. 7 shows a flowchart of the operations for activating the startphase of the method.

DETAILED DESCRIPTION OF THE INVENTION

In a vehicle of the type described above in reference to FIG. 1, theactuation of the stop & start function in a moving vehicle is managed,namely the logic managing the function is able to evaluate instant byinstant the possibility of stopping the thermal engine while the vehicleis moving if the enabling conditions are fulfilled. In the same way, itis able to restart the thermal engine while the vehicle is moving.

In particular, the control logic controls the engine stoppingconsidering the following variables: released accelerator pedal, vehiclespeed, road slope, battery charging status, drive of the electric motor,clutch opening, activation of the EPS system which controls the electricpower steering, forward gear engaged (Drive). Even if only one of theconditions set by the control logic is not verified, the engine stoppingis inhibited.

The starting or stopping strategy of the thermal energy may be optimizedif the following additional system/information are available, in orderto estimate the length of the stopping phase of the thermal engine withthe vehicle moving: estimate of the vehicle's payload; navigation systemprovided with electronic horizon, namely with the estimate of theprofile and of the slope of the road in front of the vehicle, whichallows to determine the time horizon in front of the vehicle.

Moreover a particular attention is devoted to the power steering.

The use of a completely electric steering actuator is known in the art,since the electric actuation is able to operate the power steering whenthe thermal engine is stopped, with any speed condition of the vehicle,both low (or zero) speed and high speed.

According to an aspect of the invention, the power steering is actuatedby means of a coupling of a hydraulic and an electric system. Thisallows the actuation of the stop & start function even at quite highspeed. At low speed the electric part alone is not enough, since therequired steering torque is high, higher than a 24V electric powersteering may provide (in case of an average and heavy vehicle the peakcan be even of 4.5 kW): in these conditions the current withdrawal fromthe 24V standard battery is too high and there is the risk ofdischarging it, above all in case of repeated manoeuvres, while whenexceeding a certain speed the required steering torque is highlyreduced: for example when exceeding 30-40 Km/h the required torque isvery low, at 5 Km/h already it reduces of 50%. On the other hand, if thethermal engine stops when the vehicle travels at low speed, thehydraulic power steering does not work, therefore in these conditionsthere would be no power steering.

Thus the stop & start function will be enabled only when the speed ishigher than a speed threshold, namely the thermal engine will not stopat a speed lower than the threshold but only at a speed higher than thethreshold, so that the only power steering intervening when exceedingthe threshold will be the electric power steering, while for a speedlower than the threshold, the thermal engine will not stop, andtherefore the hydraulic power steering will be working, ensuring ahigher steering torque.

The thermal engine is completely automatically restarted, in the sameway as for the stopping phase previously described, namely afterverifying the status of the same system variables.

With reference to FIG. 2, the control logic includes a hybrid controlunit for the functioning of the electric motor-generator, which performsa bidirectional dialogue with the vehicle control unit which dialoguesin its turn with the control unit of the thermal engine.

The indications coming from the control unit of the drive battery areavailable to hybrid control unit, including the indication of thecharging status SOC, a road slope sensor, and optionally the data comingfrom a navigation system and from the estimation of the vehicle'spayload.

The indication coming from the EPS system (Electric Power Steering) ofthe actuator of the electric power steering is also available, and willbe described in detail below.

The signals indicating the position of the accelerator pedal and of thebrake pedal are also available to the control unit. In particular, asregards the brake pedal, the indication available may be an indicationof the ON/OFF type (pedal completely released or completely pressed), ora more precise indication of the specific instant position of the pedaldue to the entity of the pressure on it.

With reference to FIGS. 4, 5, 6, and 7 the control logic of theactuation of the stop & start function in a moving vehicle is described.

FIG. 4 refers to the conditions enabling the STOP phase, wherein thethermal engine is stopped.

The enabling of the stop phase starts from the verification that at anyof the two following conditions is present, therefore the conditions areconnected by a logic OR:

the accelerator pedal is released, or the automated manual transmissionrequires a gear shifting.

While the first situation is determined by the action of the driver overthe accelerator pedal, the second is independent from the driver, anddepends on the information coming from the control unit of thetransmission, which informs that there are the conditions for a gearshifting.

After that, the system verifies if the vehicle speed is higher than athreshold value Vs (for example 35 km/h), Steering Activation Speed,namely the vehicle speed exceeding which the electric power steering maybe actuated alone; on the contrary, if the vehicle speed is lower thanthis threshold, stopping the thermal engine will stop the necessaryhydraulic contribution to the power steering.

After that the system verifies that the road slope is comprised betweentwo limit values: P1, lower limit (negative downhill slope, for example−4%),

P2, upper limit (positive uphill slope, for example +4%). In fact fornegative slopes lower than the threshold, the vehicle would risk to bein neutral on a steep downhill road, or for positive slopes higher thanthe threshold the electric motor alone would not be enough to guaranteethe drive.

Then the system verifies the activation of the EPS system which controlsthe electric power steering. The conditions in which it does notactivate are for example battery not charged enough, not enough speed,or a failure of the EPS itself. Since the hydraulic contribution to thepower steering is not available, the electric part must guarantee byitself all the torque needed for steering, therefore it is important tobe sure that the EPS is working, otherwise also the electriccontribution to the power steering would be missing.

Then the system verifies the charging status of the drive battery of theelectric motor: for example the charging level should always be higherthan a threshold SOC_(D), e.g. 40% of the maximum charging status, inorder to guarantee that the electric motor is properly powered.

Then the system verifies the clutch opening, namely the conditionwherein the thermal engine is excluded.

One last verification controls that the forward gear is engaged (Drive)and that the reverse gear is not engaged (Reverse).

If only one of the conditions mentioned above is not verified, thethermal engine stopping is inhibited and the STOP phase cannot start (NoStop & Start Driving), otherwise the STOP phase starts.

FIG. 5 refers to the action needed for the activation of the STOP phase.

When the STOP phase is activated, the gear shift is in neutral.

Then the EPS is put in the “Stop & Start Driving” mode. This is aspecial mode: since the hydraulic contribution to the power steering isnot present, because the thermal engine is stopped, the electric powersteering has to provide by itself all the torque needed for steering.

After that, the motor-generator activates the control of the speed ofrotation of the primary of the gearbox.

Now the motor-generator assumes the management of the speed of rotation(torque to the gearbox) of the primary of the gearbox, so that, when itintervenes, its speed of rotation is compatible with that of the gearboxin that moment. In fact the electric motor-generator is in constant meshwith the gearbox, but it can be energized or not energized, according towhat is needed. In order to avoid jerks when it starts meshing with thegearbox (it should be noted that the clutch is open and is upstream), ithas to adapt its initial speed of rotation with the speed of rotation ofthe gearbox.

At this point the thermal engine is stopped, and the vehicle drive isguaranteed only by the electric motor-generator.

With reference to FIG. 6, during the STOP phase the logic continuouslycontrols that the conditions allowing the drive with the electricmotor-generator alone are maintained, otherwise it determines theshifting to the START phase in order to restart the thermal engine, evenif only one of the following conditions is no longer verified.

Starting from the condition of stopped thermal engine, it verifies ifthe road slope is still comprised between the two values P1 and P2described above, then it verifies the activation of the EPS systemcontrolling the electric power steering, then it verifies the chargingstatus of the drive battery of the electric motor, whose charging levelmust be higher than the threshold SOC_(D).

After that it verifies that the instant power required to the electricmotor-generator is lower than the threshold value P_(LIMIT-Mot): thelatter is the maximum power value of the electric motor-generator, andis a constructive parameter which depends on the motor-generatorinstalled on the vehicle, for example 44 kW.

Then it verifies the instant speed of the vehicle, in particular if thespeed is higher than a first value V_(INF) or if it is lower than thefirst value but higher than a second value V_(INF)−ΔV_(MOD). For exampleV_(INF)=45 km/h e ΔV_(MOD)=10 km/h. If the vehicle speed is lower thanthese speed threshold values, it is necessary to restart the thermalengine. In order to avoid continuous transitions between the start andthe stop phases (and vice versa) when the control parameters are nearthe respective thresholds, an hysteresis should be introduced on eachvariable. According to the speed value the vehicle had before slowingdown, or also to the rapidity of the decreasing speed variation, itchooses which of the two restarting modes of the thermal engine it hasto activate, as described below.

After that it verifies if the brake pedal is completely released (OFFcondition).

Being all these conditions maintained, the drive can continue with theelectric motor-generator alone, otherwise there is the shifting to theSTART phase in order to restart the thermal engine, in the normal wayaccording to the first mode described below, otherwise by means of thesecond mode.

With reference to FIG. 7, two activation modes of the START phase arepossible.

-   -   mode “Activate Start phase—1 (Stop&Start Driving function)”:

First the gear is shifted in neutral: since the transmission is anautomated manual transmission, this shifting is automatic.

Then the clutch is closed and the thermal engine is restarted by usingthe electric motor.

Then the clutch is opened and the appropriate gear for the vehicle speedis requested to automated manual transmission.

Then the clutch is closed again.

Now the EPS system shifts to the “normal” mode, wherein the hydraulicpower steering is activated again.

-   -   mode “Activate Start phase—2 (Stop&Start Driving function)”:

The clutch is automatically operated by modulating a slight clutch slip,with the gearbox in mesh, and the thermal engine is restarted byexploiting the vehicle's inertia, since it is moving at a certain speed.

The control of the speed of rotation of the primary of the gearbox isactivated again by means of the motor-generator, which controls thevehicle speed in order to avoid jerks.

Then the clutch is opened again, and the engaging of the appropriategear is required, if a gear shifting is necessary.

Finally the clutch is closed again and the EPS system shifts to the“normal” mode, wherein the hydraulic power steering is activated again.

Therefore in the first case the clutch is opened, the thermal engine isstarted, and then the clutch is closed, while in the second case thethermal engine is restarted with the clutch closed, then the clutch isopened for a possible gear shifting, with less transitions.

In the second case the components are subject to more wear, especiallythe clutch, but the transition is faster.

Therefore the choice of the activation mode of the START phase isperformed according to the evaluation of the speed value the vehicle hadbefore slowing down or also of the rapidity of the decreasing speedvariation.

This kind of evaluation can be performed if a signal indicating theposition of the brake pedal is available, by which it is possible todetermine the braking graduality, and therefore the graduality of thespeed variation of the vehicle. Then, according to the positiongradient, for a sudden braking, namely for a fast decreasing speedvariation, the faster mode 2 is actuated, on the contrary for a slow andgradual braking it is possible to actuate mode 1.

Therefore it is possible to increase the time wherein the electric motoris working and the thermal engine is stopped.

The parameters SOC_(D), V_(INF), ΔV_(MOD), P1 and P2 may dynamicallyvary if the information on the road in front of the vehicle isavailable, being obtained by maps, calculation of the vehicle positionon a map (optional—info from the Navigation System) and or if theinformation on the vehicle payload estimation is available.

According to an aspect of the invention described above, the powersteering is actuated by means of a coupling of a hydraulic and anelectric system. A possible embodiment is illustrated in FIG. 3.

The actuation is obtained by means of a steering system formed by anelectric power steering actuator 7 keyed on the column 9 of a hydraulicsystem 8 by means of an appropriate reduction unit. A specially providedcontrol unit reads position signals, torque to the steering and vehiclespeed, and controls the electric motor of the electric power steeringwhich provides the right torque for steering the vehicle with a goodcomfort and a low effort by the driver.

The hydraulic actuator is controlled by the thermal engine, thereforewhen the latter is stopped the actuator does not work.

The electric actuator, on the contrary, is controlled by the EPS systemaccording to the following operating modes.

-   -   EPS in “Stop&Start Driving” mode: The power steering is        guaranteed only by the electric actuator keyed on the column,        since when the thermal engine is stopped the contribution of the        hydraulic system is null.    -   EPS in “Normal” mode: The power steering is formed by the        combination of the electric actuator and the hydraulic system        both being active and keyed on the same shaft (active thermal        engine). The distribution of the torque between the two        actuators may provide for example that the contribution of the        electric actuator tends to decrease as the vehicle speed        increases, since the hydraulic system is able to provide all the        necessary torque in order to obtain an optimal power steering,        while at low speed (or at zero speed) the contribution are added        to each other, since the maximum of the torque is required.

It will be apparent to the person skilled in the art that otheralternative and equivalent embodiments of the invention can be conceivedand reduced to practice without departing from the scope of theinvention.

From the description set forth above it will be possible for the personskilled in the art to embody the invention with no need of describingfurther construction details.

The invention claimed is:
 1. A power steering system for a vehicleprovided with means for actuating the a stop & start function in amoving vehicle, said vehicle being equipped with hybrid drive of theparallel type, comprising a thermal engine (1), an electricmotor-generator (2), a single clutch unit (3) placed between the twoengines, a transmission system (6) comprising an automated manualtransmission, means for enabling a stop phase, activating the stopphase, maintaining of the stop phase, activation of a start phase, thesystem comprising a hybrid power steering with the coupling of ahydraulic power steering controlled by the thermal engine, and anelectric power steering, controlled by an electrical power steeringcontrol system (EPS) so that, in a first mode, when a vehicle speed ishigher than a threshold value said thermal engine is stopped and saidhydraulic power steering is excluded, the electric power steeringremaining active.
 2. The power steering system as in claim 1, whereinsaid electric power steering comprising an electric steering actuator(7) keyed, by means of a reduction unit, on a column (9) of a hydraulicsystem (8) of said hydraulic power steering, being also provided acontrol unit which reads position signals, torque to the steering, andthe vehicle speed, and controls said electric steering actuator whichprovides the steering torque.
 3. The power steering system as in claim1, wherein said electric power steering control system (EPS) comprisesmeans for actuating: said first mode, wherein the power steering isguaranteed only by the electric steering actuator, when the thermalengine is stopped and the contribution of the hydraulic system is null;and a second mode, wherein the power steering is obtained by combiningthe electric steering actuator and the hydraulic system both beingactive.
 4. The power steering system as in claim 3, wherein in saidsecond mode, the torque split between the electric steering actuator andthe hydraulic system provides that the contribution of the electricsteering actuator tends to decrease as the vehicle speed increases, andthat the hydraulic system gradually provides all the necessary torque,while at low speed, or at zero speed, the contribution are added to eachother.